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annotate Doc/libthread.tex @ 3216:d00a79ebb027 legacy-trunk

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Added missing imgpbm and imgsgi modules
author Jack Jansen <jack.jansen@cwi.nl>
date Thu, 12 Oct 1995 10:23:27 +0000
parents 9b7e6d9a528d
children 3468ea8645ca
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1 \section{Built-in Module \sectcode{thread}}
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2 \bimodindex{thread}
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3
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4 This module provides low-level primitives for working with multiple
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5 threads (a.k.a.\ \dfn{light-weight processes} or \dfn{tasks}) --- multiple
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6 threads of control sharing their global data space. For
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7 synchronization, simple locks (a.k.a.\ \dfn{mutexes} or \dfn{binary
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8 semaphores}) are provided.
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9
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10 The module is optional and supported on SGI IRIX 4.x and 5.x and Sun
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11 Solaris 2.x systems, as well as on systems that have a PTHREAD
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12 implementation (e.g.\ KSR).
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13
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14 It defines the following constant and functions:
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15
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16 \renewcommand{\indexsubitem}{(in module thread)}
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17 \begin{excdesc}{error}
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18 Raised on thread-specific errors.
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19 \end{excdesc}
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20
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21 \begin{funcdesc}{start_new_thread}{func\, arg}
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22 Start a new thread. The thread executes the function \var{func}
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23 with the argument list \var{arg} (which must be a tuple). When the
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24 function returns, the thread silently exits. When the function
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25 terminates with an unhandled exception, a stack trace is printed and
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26 then the thread exits (but other threads continue to run).
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27 \end{funcdesc}
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28
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29 \begin{funcdesc}{exit}{}
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30 This is a shorthand for \code{thread.exit_thread()}.
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31 \end{funcdesc}
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32
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33 \begin{funcdesc}{exit_thread}{}
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34 Raise the \code{SystemExit} exception. When not caught, this will
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35 cause the thread to exit silently.
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36 \end{funcdesc}
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37
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38 %\begin{funcdesc}{exit_prog}{status}
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39 %Exit all threads and report the value of the integer argument
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40 %\var{status} as the exit status of the entire program.
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41 %\strong{Caveat:} code in pending \code{finally} clauses, in this thread
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42 %or in other threads, is not executed.
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43 %\end{funcdesc}
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44
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45 \begin{funcdesc}{allocate_lock}{}
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46 Return a new lock object. Methods of locks are described below. The
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47 lock is initially unlocked.
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48 \end{funcdesc}
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49
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50 \begin{funcdesc}{get_ident}{}
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51 Return the `thread identifier' of the current thread. This is a
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52 nonzero integer. Its value has no direct meaning; it is intended as a
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53 magic cookie to be used e.g. to index a dictionary of thread-specific
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54 data. Thread identifiers may be recycled when a thread exits and
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55 another thread is created.
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56 \end{funcdesc}
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57
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58 Lock objects have the following methods:
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59
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60 \renewcommand{\indexsubitem}{(lock method)}
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61 \begin{funcdesc}{acquire}{\optional{waitflag}}
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62 Without the optional argument, this method acquires the lock
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63 unconditionally, if necessary waiting until it is released by another
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64 thread (only one thread at a time can acquire a lock --- that's their
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65 reason for existence), and returns \code{None}. If the integer
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66 \var{waitflag} argument is present, the action depends on its value:\
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67 if it is zero, the lock is only acquired if it can be acquired
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68 immediately without waiting, while if it is nonzero, the lock is
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69 acquired unconditionally as before. If an argument is present, the
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70 return value is 1 if the lock is acquired successfully, 0 if not.
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71 \end{funcdesc}
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72
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73 \begin{funcdesc}{release}{}
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74 Releases the lock. The lock must have been acquired earlier, but not
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75 necessarily by the same thread.
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76 \end{funcdesc}
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77
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78 \begin{funcdesc}{locked}{}
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79 Return the status of the lock:\ 1 if it has been acquired by some
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80 thread, 0 if not.
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81 \end{funcdesc}
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82
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83 {\bf Caveats:}
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84
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85 \begin{itemize}
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86 \item
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87 Threads interact strangely with interrupts: the
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88 \code{KeyboardInterrupt} exception will be received by an arbitrary
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89 thread. (When the \code{signal} module is available, interrupts
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90 always go to the main thread.)
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91
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92 \item
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93 Calling \code{sys.exit()} or raising the \code{SystemExit} is
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94 equivalent to calling \code{thread.exit_thread()}.
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95
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96 \item
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97 Not all built-in functions that may block waiting for I/O allow other
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98 threads to run. (The most popular ones (\code{sleep}, \code{read},
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99 \code{select}) work as expected.)
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100
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101 \end{itemize}